When a radar apparatus detects an upper object under which a vehicle can pass through, such as a pedestrian bridge, or an on-road object above which a vehicle can pass through without any trouble, such as a lid of a manhole, there may be probability that alarm control or deceleration control is performed uselessly if such an object is regarded as an obstacle. In order to reduce such a probability, Japanese Laid-open Patent Publication No. 2014-6071 discloses an apparatus that calculates power of received waves and a distance from a radar apparatus to an object based on an output of the radar apparatus, calculates a correlation coefficient between the power and the distance, and determines that the object detected by the radar apparatus is an upper object under which a vehicle can pass through upon the calculated correlation coefficient falling within a predetermined range.
In the case of an upper object (merely referred to as “an upper object”, hereinafter) under which a vehicle can pass through, such a trend can be seen that the power of the received waves at the radar apparatus decreases as the distance between a host vehicle and the object decreases. On the other hand, the trend does not easily appear in the case where the object is not an upper object. Japanese Laid-open Patent Publication No. 2014-6071 utilizes such findings to determine whether the object is an upper object. However, the upper object may have various shapes, sizes, etc., and thus there may be objects that cannot be determined as upper objects, depending on the shapes, etc., of the objects.
Determining an object (also referred to as “passable object”, hereinafter) through which the host vehicle can pass as an obstacle, which may cause an execution of control (also referred to as “predetermined control”, hereinafter) for reducing the collision probability between an obstacle and the host vehicle, such as an alarm control, a deceleration control, and a stop control, becomes problematic when the radar apparatus simultaneously detects two objects (i.e., a first object and a second object) with different distances and one of the objects, which is closer to the host vehicle, is the passable object. This is because, when the predetermined control is executed uselessly in a situation where there is an obstacle such as a preceding vehicle ahead of a passable object, a driver may believe that the predetermined control is executed with respect to the obstacle and thus may not believe that the predetermined control is executed in error. In this case, the driver may easily feel strange because the obstacle exists at the position where the predetermined control is not executed in a normal state. On the other hand, in a situation where there is not an obstacle and only the passable object exists, the driver may easily understand that the predetermined control is executed in error. Further, in a situation where there is the passable object ahead of the obstacle, the predetermined control is to be executed with respect to the obstacle prior to the passable object, which is not problematic.
Therefore, an object of the disclosure is to reduce a probability of execution of a predetermined control for reducing a probability of a collision with respect to a passable object in a situation where a first object and a second object are detected simultaneously by a radar apparatus and the first object, which is closer to a host vehicle than the second object, is a passable object.